Should I upgrade? from 2 to 4 channel amp.

[Moofs]

Hey guys so I currently have a toyota corolla running 4 clarion speakers off the deck and an alpine amp with a pioneer sub. It's a single 12. Well I want to upgrade my audio even more, especially the speakers. I was gonna wait til I get a new car to pimp my audio system to something awesome since this car is old but I just had a change of plans on where I'm going to school so I thought I might as well just upgrade a little more on this since I'll be keeping it for a long time. Here are my plans:

Before I start I'm curious if you think this is a good idea and if this can make a decent reliable setup. Reliablity is key since I dont want something so shitty it'll overheat and break. anyway, back to the plan:

Clarion headunit (I have it)

Currently running a 4g amp kit.

Running sealed 12inch box.

(Sell current sub and amp and front speakers, maybe even rear too)

I've come up with this setup:

$115 Hifonics HFi55.4 amp

$125 DLS Classic C4 components

$55 Orion Cobalt CO124S sub

Total: 295

Finally, my headunit only has one set of RCA outputs so I figure I'll get this set of RCA adapters, put 1 into each out on the back of the headunit and then run the 2 sets of RCA's to the amp. Is this how you set it up?

Adaptors:

http://www.audiosavings.com/products/RCA-Cable/2-NEW-ATREND-BLUE-RCA-Y-ADAPTER-CABLES-MALE-TO-2-FEMALE/(2)+BW-Y2FB.aspx

Extra RCA:

http://www.audiosavings.com/products/RCA-Cable/NEW-ATREND-2-CHANNEL-6-FOOT-BLUE-RCA-INTERCONNECT-CABLE/BW-RCB06.aspx

And I'll wire all the speakers from the amp in the trunk to the doors with monster 16g wire. Is this okay?

okay, so what do you guys think? Is any setup dramatically better than the other. I'm gonna not amp the rear speakers, I might even take them out completely.

[Moofs]

anyone? Do you think its worth it and am I correct in setting up the cables for another set of RCA's? Idk if I should do 1 RCA cable and split it at the amp or if I should do 2 RCA's and split the amp outs at the HU. Which is better?